1. Technical Field
The present invention relates to in-vehicle power supply devices that have a function of recovering their regenerative electric power.
2. Background Art
In recent years, vehicles have been developed which have a function of recovering power during deceleration for fuel savings. For such vehicles, a variety of in-vehicle power supply devices for use in vehicles have been proposed. FIG. 7 is a schematic diagram of in-vehicle power supply device 501 disclosed in Patent Literature 1. Engine 131 of the vehicle is mechanically connected to tires 133 and electric generator 135. Electric generator 135 is electrically connected to battery 137 and vehicle electric load 139. Vehicle electric load 139 includes a starter. Electric generator 135 is electrically connected to electric double-layer capacitor 143 via DC/DC converter 141. DC/DC converter 141 is controlled by electronic processor 145.
An operation of in-vehicle power supply device 501 will be described below. Regenerative electric power is produced by driving electric generator 135 during a period of deceleration of the vehicle. Then, electronic processor 145 controls DC/DC converter 141 to charge electric double-layer capacitor 143. As a result, the regenerative electric power is stored in electric double-layer capacitor 143. After that, upon finishing the deceleration of the vehicle, electronic processor 145 controls DC/DC converter 141 to discharge electric double-layer capacitor 143 to battery 137. As a result, the regenerative electric power stored in electric double-layer capacitor 143 is supplied to battery 137 and vehicle electric load 139, which allows fuel savings of the vehicle.
In-vehicle power supply device 501 shown in FIG. 7 can provide an effective utilization of the regenerative electric power. Electronic processor 145 allows the regenerative electric power to be stored in electric double-layer capacitor 143 during the deceleration of the vehicle. After finishing the deceleration of the vehicle, and during an operation (such as acceleration, constant-speed travelling, and idling) beside deceleration, electronic processor 145 controls DC/DC converter 141 to discharge electric double-layer capacitor 143 to battery 137. Therefore, DC/DC converter 141 always operates during usage of the vehicle. Electronic processor 145 operates DC/DC converter 141 such that the voltage of electric double-layer capacitor 143 is held at the withstand voltage to prevent overcharge of the capacitor after electric double-layer capacitor 143 has been charged up to the withstand voltage thereof. Similarly, when discharging electric double-layer capacitor 143, electronic processor 145 operates DC/DC converter 141 such that the voltage of electric double-layer capacitor 143 is held at a lower limit voltage of the capacitor to prevent over-discharge of the capacitor. This operation produces a period during which DC/DC converter 141 operates only for holding the voltage of electric double-layer capacitor 143. During the period, electric double-layer capacitor 143 are neither charged nor discharged, the power consumed for operating DC/DC converter 141 is wasted, resulting in a decrease in total efficiency of the vehicle.